1. Field of the Invention
The present invention relates to an optical module such as an optical branching filter or a light switch in WDM communication and an optical module unit forming the optical module.
2. Description of the Prior Art
A schematic structure of an optical branching filter for use in WDM communication disclosed in Japanese Unexamined Patent Publication No. 2001-142102 and the like is shown in FIG. 8. An outgoing light from an outgoing side optical fiber 100 is collimated by a lens 101 to have parallel light. This parallel light is then sent to a branching filter 102. Only light with a wavelength of λi is transmitted through the branching filter 102. The transmitted light with the wavelength λi is then condensed by a lens 103 and enters an incoming side optical fiber 104. The light with remaining wavelength (λ1, λ2 . . . λn−λi) reflected at the branching filter 102 returns again to the outgoing side optical fiber 100 through the lens 101.
FIG. 8 shows a principle of structure. Practically, as shown in FIG. 9, it is necessary to cause the light (λ1, λ2 . . . λn−λi) with remaining wavelength reflected at the branching filter 102 to enter the other optical fiber 105 and take it out. In this case, it is not possible to hold optical fibers 100, 104 and 105 at right angles to optical fiber blocks 106, 107. Thus, the optical fibers 100, 104, and 105 must be inserted obliquely into the optical fiber blocks 106, 107.
Obliquely inserting the optical fibers into the optical fiber blocks makes the assembly difficult and no adjustment can be made.
Now, as shown in FIG. 10, it has also been considered to hold the optical fibers 100, 104 and 105 perpendicular to the optical fiber blocks 106, 107 by employing refractive index distribution type rod lenses 108, 109.
By employing the refractive index distribution type rod lens, it is possible to make all the optical axes of optical fibers parallel, but in the case where there are many input and output, there is a problem that it is difficult to arrange each rod lens precisely.